johndiver999
Contributor
There are other advantages as well. If you should have a back mounted pony and develop a failure behind your neck, say an o-ring extrusion, LP hose failure or something less likely. How do you determine quickly and reliably when you are solo, whether it is the primary or the pony bottle that has "sprung a leak"? It may not be obvious or instantaneously distinguishable.Where is the best place for a stage/pony?
In the front makes it more versatile. You could donate the stage - breathe from it for part of your dive and save more back gas or not breath from it and it there for back up only.
Another advantage is that a slung bottle will always have an spg that the diver can read and in a real emergency and on the ascent, it will be much more comforting to know your remaining gas supply, versus a back mounted pony that you are guessing about (unless you are running a redundant SPG for the pony you can read remotely or on a long spg hose).
Another advantage worth mentioning is that if you are ascending on the pony bottle and it starts to freeflow, or maybe an oring starts leaking or a hose gets a leak, you are pretty much SOL, if it is back mounted. If it is rigged as a stage, you can feather the valve on and off and drastically reduce any unnecessary gas loss.
These advantages are much more significant than the benefit of being able to "hand off" your pony bottle to the imaginary ghost diver who appears during a solo dive.
Regardless of these and other advantages, the OP is NOT slinging the bottle. He just asked about the third second stage - with a back mounted pony.